Nerve Conduction Studies and Electromyography for Beginners to understand basic procedure and interpretations. It can be used as a basic guideline and advance interpretation can be easily understood after you read it.

1. EMG and NCV

2. Objective
To familiarize Nerve Conduction Studies & Needle Electromyography as
diagnostic tools and interpret its findings
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3. Contents
1. Background
2. Basic Instrumentations
3. Sensory and Motor Nerve Conduction Studies
4. Late responses
5. Electromyography
6. Clinical Interpretations
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4. Electrodiagnosis
• Electrodiagnosis is the field of study that uses electrical technology to
study human neurophysiology. (Adam et al, 2020)
Types
• Conventional Electrodiagnostic Test
• Modern Diagnostic Tests
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5. Conventional Electrodiagnostic Test
Strength Duration Curve
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Rheobase Test
Chronaxie Test
Faradic/Galvanic Test
Reaction of Degeneration Test
Pulse Ratio
Accommodation
Galvanic Tetanus Ratio

6. Modern Electrodiagnostic Test
Electromyography (EMG)
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Nerve Conduction Velocity (NCV)
Late Response
Repetitive Nerve Stimulation
Evoked Potential Studies

7. Indication of EMG & NCV
1. Suspected Neuromuscular diseases
• Nerve root pathology
• Nerve/Plexus pathology
• Neuromuscular junction pathology
• Muscle pathology
2. Follow up
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Jay M Weiss, Lyn D Weiss. Easy EMG. Boston (USA): Elsevier; 2016.

8. Instrumentations
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9. Electrodes
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Surface Electrodes
Disc Ring Ground

10. Electrodes
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Stimulating Electrodes

11. Electrodes
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Concentric Monopolar Bipolar Concentric
Needle Electrodes

12. Processing Unit
Amplifier
Filter
Signal Averager
Analog to Digital Conversion
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13. Display System
1. Video Computer screen
2. Audio System
Sweep speed: Horizontal screen=
milliseconds
Sensitivity: vertical axis= response
amplitude
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14. Nerve Condition Studies
Test used to measure the speed of the electrical activity of a nerve
Nerve conduction studies can test sensory or motor nerve fibers and can
determine both the speed of conduction as well as the amplitude of the
electrical signal evoked following stimulation of a nerve. (Julie K et al, 2016)
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15. Nerve Condition Studies
Types
1. Sensory Nerve Condition Studies
2. Motor Nerve Conduction Studies
3. Late Responses- (F- wave & H- reflex)
4. Repetitive Nerve Stimulation
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16. Nerve Condition Studies
Advantage
1. Differentiate Axonal loss from demyelination
2. Localizes the site of injury
3. Can assess severity of nerve lesion
4. Can distinguish the type of nerve lesion
5. Non invasive technique
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Jay M Weiss, Lyn D Weiss. Easy EMG. Boston (USA): Elsevier; 2016.

17. Nerve Condition Studies
Limitations
1. Routine studies primarily evaluate distal nerves
2. Very Mild axon loss without demyelination may not be detected.
3. Some deeper nerve branches cannot be easily tested.
4. It does not evaluate small fibers
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Jun Kimura. Electrodiagnosis in Nerve and Muscles fourth edition. Kyoto (JAP): oxford; 2012.

18. Nerve Condition Studies
Patient Preparation:
Informed Consent
Examine skin
Relaxed comfortable position
True Nerve length
Maintain skin temperature
Clean the skin with alcohol swab
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19. Nerve Condition Studies
Stimulation:
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Orthodromic Stimulation Antidromic Stimulation
Physiological direction

20. Nerve Condition Studies
Distance Measurement:
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21. Sensory Nerve Condition Studies
Basic Principle of Nerve Stimulation
1. Sensory nerve is stimulated at one point where as Motor nerve is stimulated at
least 2 points along its course
2. Supramaximal stimulation is applied for Sensory Nerve Action Potential (SNAP)
and Compound Motor Action Potential (CMAP)
3. Cathode pole of electrode (Black) should be placed near to the active electrode
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Jun Kimura. Electrodiagnosis in Nerve and Muscles fourth edition. Kyoto (JAP): oxford; 2012.

22. Sensory Nerve Condition Studies
Electrode Placement : Sensory NCV
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Electrode Site
Active (Recording) Over the nerve
Reference 3-4 cm apart from
Active electrode
Stimulating
electrode
Along the course
of nerve to be
stimulated
Ground Between Active
and stimulating
Electrode

23. Motor Nerve Condition Studies
Electrode Placement: Motor NCV
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Electrode Site
Active
(Recording)
Over the muscle belly (motor
point)
Reference (E2
or G2)
Nearby Tendon or bone away
from the muscle
Stimulating
electrode
Along the course of nerve to
be stimulated
Ground Between Active and
stimulating Electrode

24. Nerve Condition Studies
Sensory Nerve Action Potential (SNAP)
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Compound Motor Action Potential (CMAP)

25. Nerve Condition Studies
1. Latency:
 Time taken electrical impulse to travel from the
stimulation site to the recording site
 Sensory Nerve: Depends upon the speed of
conduction of the fastest fiber and distance
between stimulus to active electrodes
 Motor Nerve: Depends upon the speed of
conduction of the fastest fiber , distance
between stimulus to active electrodes,
neuromuscular transmission time and
propagation time along the muscle membrane.
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26. Nerve Condition Studies
2. Duration :
Measured from initial
negative peak to return to
baseline
Suggest the number of
nerve fiber
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27. Nerve Condition Studies
3. Amplitude:
Measured from baseline to
negative peak or negative
peak to positive peak
Suggest the density of nerve
fiber in Sensory NCS and
number of motor units in
Motor NCS.
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28. Nerve Condition Studies
4. Nerve Conduction Velocity (NCV):
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Distance between Active and stimulating electrode
onset latency
SNCV =
Distance between proximal and distal Stimulating site
Proximal latency- distal latency
MNCV =

29. Normative value :Amplitude
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Sensory
NCV
Nerve Amplitude
(micro Volt)
Nerve Amplitude
(micro Volt)
Median (S) >20.0 Sural (S) >10.0
Ulnar (S) >18.0 Lat Femoral
Cutaneous
10-25
Radial (S) >10.0 Superficial
fibular (S)
10-26
Motor NCV
Nerve Amplitude
(m Volt)
Nerve Amplitude
(m Volt)
Median (M) >4.0 Fibular >2.0
Ulnar (M) >4.0 Medial Plantar >3.0
Radial (M) >3.0 Lateral plantar >3.0

30. Normative Value :NCV
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Sensory CV
Nerve Velocity (m/s) Nerve Velocity (m/s)
Median (S) >45.0 Sural (S) >36.0
Ulnar (S) >45.0 Lat Femoral
Cutaneous
> 44
Radial (S) >44.0 Superficial
fibular (S)
45.5-56.9
Motor CV
Nerve Velocity (m/s) Nerve Velocity (m/s)
Median (M) >50.0 Fibular >40.0
Ulnar (M) >50.0 Medial Plantar > 40.0
Radial (M) >50.0 Lateral plantar >40.0

31. Normative Value :Distal Latency
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Sensory CV
Nerve Latency (ms) Nerve Latency (ms)
Median (S) <1.9 Sural (S) <3.8
Ulnar (S) <3.1 Lat Femoral
Cutaneous
<2.6
Radial (S) <3.4 Superficial
fibular (S)
<2.4
Motor CV
Nerve Velocity (m/s) Nerve Velocity (m/s)
Median (M) <4.2 Fibular <5.5
Ulnar (M) <3.4 Medial Plantar <6.0
Radial (M) <2.9 Lateral plantar <6.0

32. To Memorize
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Nerve Upper limb Lower Limb
Latency <4.0 ms <6.0 ms
Sensory Amplitude >10.0 µV >10.0 µV
Motor Amplitude >4.0 mV >3.0 mV
NCV 40-50 m/s 35-45 m/s

33. H Reflex
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 Monosynaptic reflex
 Assess proximal lesions
 Submaximal stimulation
 Involves sensory and motor neurons
 Reflex arch of H Reflex:
• Ia sensory fiber
• Spinal cord and its interneuron
• Efferent motor fiber
Supramaximal stimulation: No H-
reflex

34. H Reflex
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Normal value in Soleus H
reflex in adults
• Latency (ms): 30.3 ± 1.7
• Amplitude (mV): 9.8 ± 6.1
• M-wave (mV): 24.6 ±6.6
• HM ratio: 0.4 ± 0.2
Clinical Implications
• Evaluates proximal sensory & motor
pathways
• GBS: absent, delayed or dispersed
• S1 radiculopathy: delayed or absent

35. F Wave
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 Supramaximal stimulation
 No reflex arch
 Evaluates
 Root or plexus abnormalities
 Neuropathy
 myopathy
 Helpful in diagnosis of
 GBS
 Thoracic outlet syndrome
 Brachial plexus injury
 Radiculopathies with more than
one root involved

36. F Wave
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Properties
1. Latency (ms): 16.3 ± 1.9
2. Amplitude(mV): 0.2 ± 0.1
3. Duration (ms): 7.6 ± 1.4
4. F –M ratio: 0.8-0.2
5. Chronodispersion: 2.5 ±1.1

37. Interpretation of NCV Studies
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Normal
Axonal Degeneration
Demyelinating
Wrist
Elbow

38. Gullian Barre Syndrome
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INCREASED
REDUCTION
PROXIMAL LATENCY
CMAP
AMPLITUDE

39. Diabetic neuropathy
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DISTAL LATENCY
CMAP AMPLITUDE
SNAP AMPLITUDE
NORMAL OR
NEAR NORMAL
REDUCTION
REDUCTION

40. Radiculopathy
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CMAP AMPLITUDE
F WAVE
H REFLEX REDUCED/ABSENT
REDUCTION
REDUCED/ABSENT

41. Pronater teres syndrome
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PROXIMAL LATENCY AT
FOREARM
DISTAL LATENCY AT
WRIST
CMAP AMPLITUDE
FOREARM
WRIST
PROLONGED
NORMAL
NORMAL

42. Variables affecting NCV Studies
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Physiological Variables Technical variables
Age Stimulating system
Temperature Recording System
Upper limb vs Lower limb Inadvertent stimulation of
another nerve
Gender Anomalous innervation of
muscles

43. Electromyography (EMG)
• Recording of action potential of muscle fibers firing singly or in a group, near the
needle electrode in a muscles (Mishra & Kalita, 2014)
• EMG test the integrity of entire motor system, which consists of upper and lower
motor neurons, neuromuscular junction and muscles (Kimura, 2016)
• Performed as an extension of physical examination rather than laboratory
procedure.
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44. Electromyography (EMG)
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NEEDLE EMG
SURFACE EMG

45. Special Precautions for EMG
• Morbid Obesity
• Thin Individuals
• Bleeding disorders
• Aseptic precaution
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46. Contraindication for EMG
• Recent systemic infectious diseases
• Recent muscle biopsy
• Localized inflammation
• Skin lesions
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47. EMG Procedure
• Preparation of patient
• Select the muscles to be tested
• Locate the site of needle insertion
• Insert the needle quickly
• Sharp Motor Unit Potential (MUP) on minimal voluntary contraction
confirms that needle is in proper position. If MUP is not sharp,
reposition the needle
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48. Neuropathy vs Myopathy
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Neuropathy Myopathy
Number of motor neuron decreases Muscle fibers are destroyed
Deprived muscles fibers get collateral from
viable motor neuron
Decreased number of muscle fibers
supplied by a single motor neuron
Increased number of muscle fibers supplied
by a single motor neuron
Decrease in size of motor unit
Amplitude and duration of Motor unit action
potential increases
Amplitude and duration of Motor unit
action potential decreases

49. EMG Analysis
1. Insertional Activity
2. Muscles at Rest
3. Motor Unit Analysis on mild voluntary contraction
4. Maximum voluntary contraction
• Recruitment pattern
• Interference pattern
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50. Insertional activity
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51. Insertional activity
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52. Insertional activity
Insertional activity Seen in
Increased Early stage of denervation
Acute myositis
Inflammatory myopathies
Decreased Atrophied muscles
Fibrosed muscles
Needle electrode is not in
muscle tissue
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53. Examination of Muscles at Rest
1.No activity
2. Endplate region:
1. Miniature Endplate
Potentials (MEEP)
2. Endplate spike
3. Spontaneous Activity
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54. Examination of Muscles at Rest
Endplate region:
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55. Spontaneous Activity
Originated from Muscle Fibers Originated from motor neuron
1.Fibrillation Potentials (Fibs)
2.Positive sharp waves (PSW)
3.Myotonic Discharge
4.Complex repetitive discharges
1.Myokymic discharge
2.Cramps
3.Neuromyotonic discharge
4.Fasciculation
5.Fibrillation Potentials (Fibs)
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56. Spontaneous activities
1. Positive Sharp Wave
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Seen in:
1. Mainly on Lower Motor
Neuron Lesion
2. Also seen in Myopathies

57. Spontaneous activities
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2. Fibrillation Potential Seen in
1. LMNL
2. Myopathies

58. Spontaneous activities
Positive Sharp Wave and Fibrillation Potential
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59. Spontaneous Activity
3. Complex Repetitive Discharge (CRD)
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Seen in
Myogenic conditions
Polymyositis
Muscular dystrophies
Neurogenic Conditions
Poliomyelitis
ALS
Chronic radiculopathies
Chronic neuropathies

60. Spontaneous Activity
3. Complex Repetitive Discharge (CRD)
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61. Abnormal Spontaneous Activity
Seen in
Myotonic dystrophy
Polymyositis
Chronic radiculopathy
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4. Myotonic discharge

62. Abnormal Spontaneous Activity
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4. Myotonic discharge

63. Abnormal Spontaneous Activity
5. Myokymic discharge
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Seen in
Facial Muscles:
Bells palsy
Multiple sclerosis
Polyradiculopathy
Limb muscles
Chronic nerve lesions

64. Abnormal Spontaneous Activity
5. Myokymic discharge
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65. Abnormal Spontaneous Activity
6. Fasciculation
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Seen in
Small twitch
Irritation of AHC
Chronic peripheral nerve lesions
Nerve root compression
Muscle spasm or cramps
ALS and PMA (motor neuron
diseases)

66. Abnormal Spontaneous Activity
6. Fasciculation
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67. Motor Unit Action Potential (MUAP)
• Analysis of MUAP done with
minimal contraction of muscles
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68. Motor Unit Action Potential (MUAP)
Component Normative value
Amplitude 4 µV to 5 mV
Duration 2 ms to 17 ms
Rise time Upto 500 ms
Frequency 1 Hz- 60 Hz
Phase Mono to Four
phases
(Bi-phasic or Tri-
phasic)
Sound Clear, sharp
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69. Motor Unit Action Potential (MUAP)
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70. Motor Unit Action Potential (MUAP)
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Amplitude and Duration
Increased in Neuropathy
Decreased in myopathy

71. Motor Unit Action Potential (MUAP)
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Phases
Normal triphasic
Polyphasic
+ Longer
Duration
Neurogenic abnormalities
+ Shorter Myopathic

72. Examination of Muscles at Maximum
Voluntary Contraction
• Change in electrical activity during progressively increasing
contraction to maximal contraction
1. Recruitment
2. Interference pattern
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73. Recruitment & Interference
• The motor unit start firing in a regular pattern at 5 Hz
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Normal
Neurogenic
Myopathic

74. Normal Interference Pattern
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75. Myopathy Interference Pattern
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76. Neurogenic Interference Pattern
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77. EMG finding in DMD
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DECREASED/ ABSENT
Fibrillation Potential, Positive sharp waves
Low amplitude, Short duration, Polyphasic
Low amplitude and Reduced
Insertional Activity
Spontaneous
Activity
Motor Unit Potential
Interference

78. EMG finding in Gullian Barre Syndrome
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Increased
Fasciculation or Myokymic
High amplitude, long duration, Polyphasic
High amplitude and Reduced
Insertional Activity
Spontaneous
Activity
Motor Unit Potential
Interference

79. Role of EMG and NCV Tests in Physiotherapy
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EVALUATE TREATMENT OUTCOME
NEUROMUSCULOSKELETAL ASSESSMENT
PLAN PHYSIOTHERAPY INTERVENTION

80. Take Home Message
1. NCV : demyelinating and axonal neuropathy
2. Late responses (F wave and H-reflex) : Radiculopathy and proximal neuropathy
3. Electromyography studies differentiates myopathy with neuropathy
4. All these tests are extensions of physical examinations
5. Findings of Electrodiagnosis tests can be valuable to plan physiotherapy
interventions based on severity and type of neuromusculoskeletal injuries
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81. THANK YOU
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